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53 lines
1.7 KiB
Go
53 lines
1.7 KiB
Go
package goldilocks
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import fp "github.com/cloudflare/circl/math/fp448"
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func (Curve) pull(P *twistPoint) *Point { return twistCurve{}.push(P) }
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func (twistCurve) pull(P *Point) *twistPoint { return Curve{}.push(P) }
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// push sends a point on the Goldilocks curve to a point on the twist curve.
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func (Curve) push(P *Point) *twistPoint {
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Q := &twistPoint{}
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Px, Py, Pz := &P.x, &P.y, &P.z
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a, b, c, d, e, f, g, h := &Q.x, &Q.y, &Q.z, &fp.Elt{}, &Q.ta, &Q.x, &Q.y, &Q.tb
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fp.Add(e, Px, Py) // x+y
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fp.Sqr(a, Px) // A = x^2
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fp.Sqr(b, Py) // B = y^2
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fp.Sqr(c, Pz) // z^2
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fp.Add(c, c, c) // C = 2*z^2
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*d = *a // D = A
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fp.Sqr(e, e) // (x+y)^2
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fp.Sub(e, e, a) // (x+y)^2-A
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fp.Sub(e, e, b) // E = (x+y)^2-A-B
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fp.Add(h, b, d) // H = B+D
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fp.Sub(g, b, d) // G = B-D
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fp.Sub(f, c, h) // F = C-H
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fp.Mul(&Q.z, f, g) // Z = F * G
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fp.Mul(&Q.x, e, f) // X = E * F
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fp.Mul(&Q.y, g, h) // Y = G * H, // T = E * H
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return Q
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}
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// push sends a point on the twist curve to a point on the Goldilocks curve.
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func (twistCurve) push(P *twistPoint) *Point {
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Q := &Point{}
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Px, Py, Pz := &P.x, &P.y, &P.z
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a, b, c, d, e, f, g, h := &Q.x, &Q.y, &Q.z, &fp.Elt{}, &Q.ta, &Q.x, &Q.y, &Q.tb
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fp.Add(e, Px, Py) // x+y
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fp.Sqr(a, Px) // A = x^2
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fp.Sqr(b, Py) // B = y^2
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fp.Sqr(c, Pz) // z^2
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fp.Add(c, c, c) // C = 2*z^2
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fp.Neg(d, a) // D = -A
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fp.Sqr(e, e) // (x+y)^2
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fp.Sub(e, e, a) // (x+y)^2-A
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fp.Sub(e, e, b) // E = (x+y)^2-A-B
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fp.Add(h, b, d) // H = B+D
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fp.Sub(g, b, d) // G = B-D
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fp.Sub(f, c, h) // F = C-H
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fp.Mul(&Q.z, f, g) // Z = F * G
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fp.Mul(&Q.x, e, f) // X = E * F
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fp.Mul(&Q.y, g, h) // Y = G * H, // T = E * H
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return Q
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}
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